Thermal fuse



' May 29, 1934. H. KERSHAW 1,960,495

THERMAL FUSE Filed. March 18, 1933 Patented May 29, 1934 UNITED STATES PATENT OFFICE 10 Claims.

My invention relates to improvements in thermal fuses.

An important object of the invention is to provide a thermal fuse having a plurality of fusible elements which may be successively brought into the operative position.

A further object of the invention is to provide means for holding and advancing the fusible elements in such a manner that they are retained in separate pockets or enclosed spaces, so that the fusing of one element will not injure the adjacent element.

A further object of the invention is to provide a thermal fuse of the above-mentioned character,

so constructed that the fusible element which is in the operative position, is clearly visible, so that its condition may be readily ascertained.

A further object of the invention is to provide a device of the above-mentioned character, which is extremely simple in construction, formed of relatively few parts, which may be quickly and easily assembled.

Other objects and advantages of the invention will be apparent during the course of the followmg description.

In the accompanying drawing, forming a part of this specification, and in which like numerals are employed to designate like parts throughout the same,

Figure 1 is a rear end elevation of a thermal fuse embodying my invention,

Figure 2 is a side elevation of the same,

Figure 3 is a central longitudinal section through the same, parts in elevation,

Figure 4 is a rear end elevation of the relatively stationary cap member,

Figure 5 is a rear end elevation of the rotary Figure 6 is a forward end elevation of the rotary plug,

Figure 7 is a side elevation of the resilient contact, associated elements being shown in section,

Figure 8 is a fragmentary plan View of the resilient contact and associated elements.

Figure 9 is a side elevation of a transparent washer,

Figure 10 is an end elevation of a connector,

Figure 11 is a rear end elevation of a plug embodying a modified form of the invention,

Figure 12 is a central longitudinal section through the same, and

Figure 13 is a side elevation of an opaque washer.

In the drawing, wherein for the purpose of il- 55 lustration is shown a preferred embodiment of my invention, the numeral 15 designates a tubular body portion of the fuse, which may be formed of any suitable insulating material, such as bakelite or the like. This tubular body portion is molded for providing screw-threads 16, as shown. The tubular body portion is provided at its rear end with a flat circular head 17, extending radially outwardly and inwardly beyond the tubular body portion 15, as shown. This head 17 is provided with a central circular opening 18, and radially outwardly of this opening with an elongated auxiliary opening or window 19, as shown. The purpose of the window is to permit of the ready inspection of the fusible element when it is brought to the operative position, as will be explained.

The numeral 20 designates a relatively stationary cap member, the rear end of which is adapted for insertion within the tubular body portion 15, and preferably having a snug fit therein. This cap member is provided with an annular flange 21, engaging over the forward end of the tubular body portion' 15, as shown. The cap member is securely held upon the tubular body portion 15 by a tubular metallic screwthreaded terminal element 22, engaging the screw-threads 16, and provided at its forward end with an inwardly bent flange 23, engaging over the flange 21, as shown. The cap member 20 is formed of any suitable insulating material, such as bakelite, or the like. This cap member is provided at its rear end with a tapered recess 24, the wall of which is preferably inclined at an angle of 45 degrees with respect to the longitudinal axis of the cap member. The recess 24, at its forward end, leads into a groove 25, in communication with a restricted opening 26, which extends through the forward end of the cap member. The groove 25 also has an extension 27, leading into the recess 24, and extending forwardly beyond the same. The resilient contact 28 is held within the opening 26, and has its forward end bent laterally into an inner terminal 29, while the free end of the contact 28 projects into the extension 27 and is shiftable laterally therein, and is tensioned to move into or toward the recess 24. This resilient contact 28 is also twisted or bent upon its longitudinal axis, affording an inclined or rounded edge 28' and a straight edge 29', for a purpose to be explained.

The numeral 30 designates a rotary plug preferably having flats 31, which are also preferably milled or roughened on the rear end portions thereof. The plug is rotatable within a circular opening 18, formed in the head 17 and pro- 110' .17 is not now provided with the window 19.

jects rearwardly beyond the same so that it may be conveniently grasped by the finger and turned thereby.

The plug is provided at its forward end with a disc or head 33, which tapers forwardly. This head is rigidly secured to the plug 30, and is arranged within the tapered recess 24. The head 33 is provided with spaced ribs or teeth 34, preferably formed integral therewith, and the outer edges of these teeth converge forwardly so that they slidably contact with the wall of the recess 24, thereby affording separate spaces 35 between the teeth.

The numeral 36 designates a fuse device as a whole, formed of fusible metal. This device embodies a ring 37, and fusible radial elements 38, carrying enlarged contact heads 39. The ring 36 is placed upon the rotatable plug 30, adjacent to the head or disc 35, and the fusible elements 38 are bent over the edge of the disc 35, so that the enlarged contact elements 39 are arranged within the tapered spaces 35. Particular atten tion is called to the fact that the fusible elements 38 are narrower than the ring 36, and each fusible element 38 will therefore, fuse before the ring 36 would fuse. Further, by virtue of the taper of the contact heads 39, and the taper of the spaces 35, each contact head is permanently retained within the space 35, and cannot fall from the same, if the element 38 thereof should fuse.

The numeral 40 designates a resilient metal connector, embodying an arm 41, formed integral with a forked contact portion 42. This forked contact portion is longitudinally bowed. The contact portion 40 is inserted upon rotatable plug 30, and the arm 41 is arranged within a groove 42, formed upon the exterior of the cap 20. The forward end of this arm is electrically connected with the screw-threaded sleeve 22, or outer terminal, by any suitable means, as by soldering. Particular attention is called to the fact that the bowed arrangement of the contact 42 causes the same to have a firm yielding engagement with the ring 36, thus insuring proper electrical connection.

A transparent washer 43, formed of mica or the like, has a central opening 44, provided with fiat walls, and this central opening receives the rotary plug 30, this washer being arranged between the forked contact 42 and the window 19, the opening 45 of the contact 42 being in alignment with the window. The washer 43 is preferably formed of mica, although it may be formed of any other suitable transparent material, and is rotatable with the plug 30. The function of this washer is to cover the window to prevent the escape of flame, spark, or gas, when the fusible element fuses, but rendering the fusible element normally fusible. When the element fuses, that portion of the transparent washer immediately adjacent to the same, becomes blackened, thus indicating that the element has fused, and when the plug is turned to the next position, the succeeding fusible element is again visible.

In Figures 11 and 12, I have shown a modified form of the invention. In these figures, the tubular body portion 15 and head 1'? are formed of transparent material, preferably glass. The head The transparent washer 43 is also omitted, and a washer 46, which may be formed of metal or the like, is substituted for the transparent washer. This washer has a short radial extension 47, which projects into the groove 42', thus preventing the washer 46 from turning, so that the opening 48 thereof is kept in alignment with the opening 45. Suitable information, indicated at 49, may be stamped or printed upon the washer 4G, and this will be visible through the transparent head 17. The fusible element 38 will be visible through the openings 45 and 48, as is obvious. All other parts of the device remain identical with those shown and described in connection with the first form of the invention.

The operation of the device is as follows:

The rotatable plug 30 is in the starting position, with the resilient contact 28 engaging one of the contact heads 39, and a circuit will be closed for electrically connecting the inner and outer terminals 22 and 29, as is obvious. The fusible element 28 now in the operative position, is visible through the window 19. Particular attention is called to the fact that the forked contact 42 has two separate arms which engage with the ring 36, at two separate points. Therefore, if a current of thirty amperes is passing through the arm 41, this is divided into fifteen amperes in two branches 42, and hence there is but fifteen amperes at each point of contact between the branches 42 and the ring 36, whereby there will be no liability of the ring 36 fusing instead of the reduced fusible element 38. Should the fusible element 38 in the operative position now fuse, this will blacken the transparent Washer 43. This will indicate that the element is fused, and the operator will turn the rotatable plug 30 to the next position, bringing the succeeding fusible element to the operative position. Since the mica washer 43 rotates with the plug, a clean portion of the Washer is presented over the next fusible element, whereby such element is again visible. This transparent washer covers the window 19, preventing flame, sparks or gas from escaping. The contact 28 is not only inclined, but is twisted or bent upon its longitudinal axis, as described, whereby the rounded edge 28' will trip over the teeth 34, but its opposite straight edge 29 will lock with the teeth. This permits of only a one-way turning movement of the rotary plug.

Having fully described my invention, what I claim is:

1. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body portion and having a forwardly tapered recess formed in its rear end, a resilient contact arranged within a portion of the recess and extending to the for ward end of the cap and terminating in an inner terminal, a rotatable plug extending through the opening in the end of the tubular body portion and provided with a head having spaced ribs which converge forwardly for slidable engagement with the wall of the tapered recess, fusible elements disposed between the spaced ribs, the resilient contact being adapted to engage with the fusible elements and the ribs, a conductor having electrical connection with the fusible elements, and an outer terminal carried by the tubular body portion and electrically connected with the conductor.

2. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body portion and having a forwardly tapered recess formed in its rear end, said cap being also provided in its rear end with a groove extending forwardly beyond the recess, a resilient contact mounted within the groove and extending to the forward end of the cap to constitute an inner terminal, a rotatable plug extending through the opening in the rear end of the tubular body portion and provided with a forwardly tapering head having spaced ribs which converge forwardly so that the ribs have slidable contact with the wall of the tapered recess, a fuse device embodying. a ring arranged upon the rotatable plug adjacent to the rear end of the head and plug and provided with radial fusible elements which are bent over the edge of the head to enter the spaces between the ribs, the resilient contact being adapted to en gage with the fusible elements and the ribs, a connector having a resilient part arranged between the head of the tubular body portion and the head of the rotatable plug and contacting with the ring, and an outer terminal carried by the tubular body portion and having electrical connection with the connector.

3. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body portion and having a forwardly tapered recess formed in its rear end, said cap being provided in its rear end with a groove leading intothe recess and extending forwardly beyond the recess, a resilient contact mounted within the groove and extending to the forward end of the cap to provide an inner terminal, a rotatable plug extending through the opening in the rear end of the tubular body portion and provided with a forwardly tapered head having spaced ribs which converge forwardly for slidable contact with the wall of the tapered recess, a fuse device embodying a ring arranged upon the rotatable plug adjacent the head of the same and having radial fusible elements bent over the edge of such head to enter the spaces between the ribs, the resilient contact being adapted to engage with the fusible elements and ribs, a connector including an arm and a pair of spaced longitudinally bowed resilient contacts connected therewith, the bowed contacts being arranged in the rear end of the tubular body portion and engaging with the ring, and an outer terminal carried by the tubular body portion and having electrical connection with the arm.

4. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body portion and having a forwardly tapered recess formed in its rear end, said cap being provided in its rear end with a groove leading into the recess and extending forwardly beyond the recess, a resilient contact for movement within the groove and bent transversely upon its longitudinal axis for affording an inclined edge and a fiat edge, said contact extending to the forward end of the cap for affording an inner terminal, a rotatable plug extending through the opening in the rear end of the tubular body portion and provided with a forwardly tapering head having spaced ribs which converge forwardly for slidable contact with the wall of the tapered recess, said resilient contact engaging with the ribs of said head so that the plug may be turned in one direction only, fusible elements carried by the head of the plug and arranged between the ribs for engagement with the resilient contact, a connector having electrical connection with the fusible elements, and an outer terminal carried by the tubular body portion and having electrical connection with the connector.

5. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening and an observation portion, an insulating cap insertable within the forward end of the tubular body portion, a plug rotatable within the opening of the end and having a head arranged within the rear portion of the tubular body portion, a fuse device including a ring mounted upon the plug adjacent to the rear end of the head and carrying radial fusible elements which extend over the periphery of the head, a resilient contact washer arranged between the head of the tubular body portion and the head of the rotatable plug and contacting with the ring and having an opening formed therein for coaction with the observation portion of the rear end of the tubular body portion, an arm electrically connected with the resilient contact washer, and an outer terminal carried by the tubular body portion and electrically connected with the arm.

6. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening and a window, an insulating cap insertable within the forward end of the tubular body portion, a plug rotatable within the opening of the end and having a head arranged within the rear portion of the tubular body portion, a fuse device including a ring mounted upon the plug adjacent to the rear end of the head and carrying fusible elements which extend over the periphery of the head, a resilient contact washer arranged within the rear end of the tubular body portion and engaging with the ring and having an opening formed therein in alignment with the window, an outer terminal carried by the tubular body portion, means electrically connecting the contact washer with the outer terminal and hold ing the contact washer against relative turning movement, an inner terminal carried by the cap, a resilient contact carried by the cap to engage with the fusible elements and electrically connected with the inner terminal, and a transparent washer mounted upon the plug and rotatable therewith and serving to cover the window.

7. A thermal fuse comprising an insulating tubular body portion having a rear end provided with a central opening and a window disposed radially outwardly of the central opening, an insulating plug insertable through the rear end of the tubular body portion and provided upon its periphery with a longitudinal groove, a plug rotatable within the central opening and having a head arranged within the rear end of the tubular body portion, a fuse device carried by the head and embodying spaced fusible elements, a resilient contact carried by the plug for coaction with the fusible element, an arm extending through the longitudinal groove, a resilient contact washer connected with the arm and disposed rearwardly of the head to engage with a portion of the fuse device, said resilient contact Washer having an opening in alignment with the window, and a transparent washer arranged within the rear end of the tubular body portion at the rear of the resilient contact washer and mounted upon the plug for rotation therewith, an inner terminal connected with the resilient contact, and an outer terminal connected with the arm.

8. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body por- 15f tion and having a recess formed in its rear end, a groove leading into the recess and extending forwardly beyond the same, a resilient contact arranged for movement within the groove, an inner terminal carried by the insulating cap and electrically connected with the resilient contact, a rotatable plug extending through the opening in the rear end of the tubular body portion and provided with a head which is arranged within said recess, said head having spaced ribs slidably engaging with the wall of the recess so that the spaces between the ribs are closed at their sides by the ribs, fusible elements disposed within the spaces between the ribs, the resilient contact being adapted to engage with the fusible elements and the ribs, a conductor having electrical connection with the fusible elements, and an outer terminal carried by the tubular body portion and electrically connected with the conductor.

9. A thermal fuse comprising an insulating tubular body portion having a rear end provided with an opening, an insulating cap insertable within the forward end of the tubular body portion and having a recess formed in its rear end and also having a groove leading into the recess and extending forwardly beyond the same, a resilient contact arranged for movement within the groove and recess, said resilient contact having a transversely inclined portion, an inner terminal carried by the insulating cap and electrically connected with the resilient contact, a rotatable plug extending through the opening in the rear end of the tubular body portion and provided with a head arranged within said recess, said head having spaced ribs which slidably engage with the wall of said recess, the ribs forming spaces which are closed at their sides by such ribs, fusible elements disposed within the spaces between the ribs, the resilient contact being adapted to engage with the fusible elements and the ribs and so coacting with the ribs that the plug can be turned in one direction only, a conductor having electrical connection with the fusible ele ments, and an outer terminal carried by the tubular body portion and electrically connected with the conductor.

10. A thermal fuse comprising an insulating tubular body portion, a member closing the forward end of the tubular body portion and provided with a forward recess and a groove leading into the recess and extending forwardly beyond the wall of the recess, a plug having a head mounted within the recess, said head having spaced ribs slidably engaging the wall of the recess so that the spaces between the ribs are separated by such ribs, fusible elements disposed within the spaces between the ribs, a resilient contact arranged for movement within the groove and recess and adapted to engage with the fusible elements and ribs, an inner terminal having electrical connection with the resilient contact, and an outer terminal having electrical connection with the fusible elements.

HENRY KERSHAW. 

